From: Menji76 | #007
That's the thing. It's not specifying. Is 'business attire' its own thing? The only thing google returns is that it might be a sports coat instead of a dress coat.
Since business casual is a very well-known term, I would think that whoever told you to wear business attire would have specified casual if that were the case.
Relevant: http://en.wikipedia.org/wiki/Informal_attire
And as you said, it's almost always better to overdress than underdress.
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